This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-333582, filed Oct. 31, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electrostatic actuator for driving a movable section arranged between a pair of stator sections by utilizing an electrostatic force (Coulomb force), particularly, to an electrostatic actuator that makes it unnecessary to use an electric wiring connected to the movable section and a camera module using the particular electrostatic actuator in the focus adjusting mechanism.
2. Description of the Related Art
An electrostatic actuator comprising a movable section arranged between a pair of stator sections, said movable section being driven by an electrostatic force (Coulomb force), is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 8-140367. The conventional electrostatic actuator disclosed in this prior art comprises a first stator section and a second stator section, which are arranged to face each other, and a movable section arranged between these first and second stator sections. A first electrode array consisting of a plurality of electrodes arranged at a predetermined pitch in the longitudinal direction is mounted to the first stator section. Also, a second electrode array consisting of a plurality of electrodes arranged at a predetermined pitch in the longitudinal direction is mounted to the second stator section. It should be noted, however, that the phase of the electrodes of the first electrode array is deviated from the phase of the electrodes of the second electrode array by a xc2xd pitch.
To be more specific, the electrodes of each of the first electrode array and the second electrode array are divided on the imaginary basis into four groups A, B, C and D, with every two electrodes in the arranging direction forming a single group, and a DC voltage is applied between the electrodes of each of these groups and the electrodes on the movable section.
In the conventional electrostatic actuator disclosed in this prior art, the driving operations (1) and (2) given below are alternately repeated:
(1) A DC voltage is applied between the first electrode array and the electrode mounted to the movable section so as to attract electrostatically the movable section toward the first stator section; and
(2) A DC voltage is applied between the second electrode array and the electrode mounted to the movable section so as to attract electrostatically the movable section toward the second stator section.
By the driving operation given above, the movable section is macroscopically moved successively in the longitudinal direction of the stator sections by xc2xd pitch of the electrode array while being vibrated microscopically between the first stator section and the second stator section. The moving direction of the movable section can be changed by changing the order of applying a DV voltage to the electrodes of groups A, B, C and D. Specifically, the movable section can be moved in a first direction by applying a DC voltage to the electrodes of groups A and B, the electrodes of groups B and C, the electrodes of groups C and D, and the electrodes of group D in the order mentioned. Also, the movable section can be moved in a second direction opposite to said first direction by applying a DC voltage to the electrodes of groups D and C, the electrodes of groups C and B, the electrodes of groups B and A, and the electrodes of group A in the order mentioned.
In the conventional electrostatic actuator, utilized is the electrostatic force generated when a DC voltage is applied between the electrode arrays on the stator sections and the electrode on the movable section so as to make it absolutely necessary to mount an electrical wiring to not only the electrode arrays on the stator sections but also to the electrode on the movable section. Since it is necessary to mount an electrical wiring to the movable section, the mass production capability of the electrostatic actuator is impaired. Also, since the space for the wiring is required, the miniaturization of the electrostatic actuator is impaired. Further, since the movable section is moved frequently, stress is applied to the wiring to the electrode on the movable section, with the result that the reliability is lowered during use of the electrostatic actuator over a long time.
It should also be noted that, in the conventional electrostatic actuator, a dielectric film is formed on the electrode as a measure against the insulation breakdown. What should be noted is that the dielectric polarization is generated in the dielectric film when a DC voltage is applied between the electrode arrays on the stator sections and the electrode on the movable section. The dielectric polarization produces the force for keeping the movable section, which is attracted to one of the stator sections, attracted to the particular stator section. The potential difference produced by the dielectric polarization is small. However, since the distance between the movable section and the stator section is small, it is possible for the force produced by the dielectric polarization to become larger than the electrostatic force produced between the electrode on the other stator section and the electrode on the movable section, with the result that the normal moving operation of the movable section tends to be obstructed.
As described above, in the conventional electrostatic actuator, in which the movable section is moved by utilizing the electrostatic force generated when a DC voltage is applied between the electrode array on the stator section and the electrode on the movable section, it is absolutely necessary to mount an electrical wiring to the electrode on the movable section so as to give rise to the problems that the mass production capability of the electrostatic actuator is lowered, that the electrostatic actuator is rendered bulky because of the requirement of the space occupied by the electrical wiring, and that the reliability of the electrostatic actuator is lowered over a long time.
In addition, the conventional electrostatic actuator gives rise to the problem that the moving operation of the movable section is rendered unstable under the influence of the dielectric polarization taking place in the dielectric film formed on the electrode as a measure against the insulation breakdown.
An object of the present invention is to provide an electrostatic actuator that makes it unnecessary to mount an electrical wiring to the movable section.
Another object of the present invention is to provide an electrostatic actuator that permits eliminating the influence given by the dielectric polarization of the dielectric film formed on the electrode so as to realize a stable operation.
Further, still another object of the present invention is to provide a camera module using the particular electrostatic actuator of the present invention in the focus adjusting mechanism.
According to a first aspect of the present invention, there is provided an electrostatic actuator, comprising:
a first stator section including a first electrode array including first, second and third electrodes arranged at a predetermined pitch in a first direction;
a second stator section arranged to face the first stator section and to define a space between the first and second stator sections, and including a second electrode array including fourth and fifth electrodes extending in the first direction;
a movable section arranged in the space and including a first electrode section facing the first electrode array and a second electrode section facing the second electrode array, the first and second electrode sections being maintained at a predetermined floating potential; and
a driving circuit configured to apply DC voltage signals to the first and second electrode arrays, alternatively, the DC voltage signal having a first level higher than the predetermined floating potential and a second level lower than the predetermined floating potential,
the first DC voltage signal being applied to the adjacent first and second electrodes of the first electrode array to attract the first electrode section of the movable section during a first period, the first and second electrodes of the first electrode array being maintained at the first and second levels during the first period, respectively,
the second DC voltage signal being applied to the fourth and fifth electrodes of the second electrode array to attract the second electrode section of the movable section during a second period, the fourth and fifth electrodes of the second electrode array being maintained at the first and second levels during the second period, respectively,
the third DC voltage signal being applied to the adjacent second and third electrodes of the first electrode array to attract the first electrode section of the movable section during a third period, the second and third electrodes of the first electrode array being maintained at the first and second levels during the third period, respectively,
the fourth DC voltage signal being applied to the fourth and fifth electrodes of the second electrode array to attract the second electrode section of the movable section during a fourth period, the fourth electrode of the second electrode array being maintained at one of the first and second levels during the fourth period, and the fifth electrode of the second electrode array being maintained at the other of first and second levels during the fourth period, and
the movable section being moved in the first direction in accordance with the application of the first, second, third and fourth DC voltage signals.
According to a second aspect of the present invention, there is provided an electrostatic actuator, comprising:
a first stator section including a first electrode array including first, second and third electrodes arranged at a predetermined pitch in a first direction;
a second stator section arranged to face the first stator section and to define a space between the first and second stator sections, and including a second electrode array including fourth, fifth and sixth electrodes arranged at the predetermined pitch in the first direction;
a movable section arranged in the space and including a first electrode section facing the first electrode array and a second electrode section facing the second electrode array, the first and second electrode sections being maintained at a predetermined floating potential; and
a driving circuit configured to apply DC voltage signals to the first and second electrode arrays, alternatively, the DC voltage signal having a first level higher than the predetermined floating potential and a second level lower than the predetermined floating potential,
the first DC voltage signal being applied to the adjacent first and second electrodes of the first electrode array to attract the first electrode section of the movable section during a first period, the first and second electrodes of the first electrode array being maintained at the first and second levels during the first period, respectively,
the second DC voltage signal being applied to the adjacent fourth and fifth electrodes of the second electrode array to attract the second electrode section of the movable section during a second period, the fourth and fifth electrodes of the second electrode array being maintained at the first and second levels during the second period, respectively,
the third DC voltage signal being applied to the adjacent second and third electrodes of the first electrode array to attract the first electrode section of the movable section during a third period, the second and third electrodes of the first electrode array being maintained at the first and second levels during the third period, respectively,
the fourth DC voltage signal being applied to the adjacent fifth and sixth electrodes of the second electrode array to attract the second electrode section of the movable section during a fourth period, the fifth and sixth electrodes of the second electrode array being maintained at the first and second levels during the fourth period, respectively, and
the movable section being moved in the first direction in accordance with the application of the first, second, third and fourth DC voltage signals.
According to a third aspect of the present invention, there is provided an electrostatic actuator, comprising:
a first stator section including first and second electrode arrays each including first, second and third electrodes and arranged substantially in parallel and at a predetermined pitch in a first direction;
a second stator section arranged to face the first stator section and to define a space between the first and second stator sections, and including a third electrode array including fourth and fifth electrodes;
a movable section arranged in the space and including a first electrode section facing the first electrode array and a second electrode section facing the second electrode array, the first and second electrode sections being maintained at a predetermined floating potential; and
a driving circuit configured to apply DC voltage signals to the first and second electrode arrays and the third electrode array, alternatively, the DC voltage signal having a first level higher than the predetermined floating potential and a second level lower than the predetermined floating potential,
the first DC voltage signal being applied to the first electrodes of the first and second electrode arrays to attract the first electrode section of the movable section during a first period, the first electrodes of the first and second electrode arrays being maintained at the first and second levels during the first period, respectively,
the second DC voltage signal being applied to the fourth and fifth electrodes of the third electrode array to attract the second electrode section of the movable section during a second period,
the third DC voltage signal being applied to the second electrodes of the first and second electrode arrays to attract the first electrode section of the movable section during a third period, the second electrodes of the first and second electrode arrays being maintained at the first and second levels during the third period, respectively, and the movable section being moved in the first direction in accordance with the application of the first, second and third DC voltage signals.
According to a fourth aspect of the present invention, there is provided an electrostatic actuator, comprising:
a first stator section including first and second electrode arrays each including first and second electrodes and arranged substantially in parallel and at a predetermined pitch in a first direction;
a second stator section arranged to face the first stator section and to define a space between the first and second stator sections, and including third and fourth electrode arrays each including third and fourth electrodes and arranged substantially in parallel and at a predetermined pitch in the first direction, the third and fourth electrode array being arranged at the same pitch as that of the first and second electrode arrays in the first direction and the arrangement of the third and fourth electrode arrays being deviated by the half of the predetermined pitch from the arrangement of the first and second electrode arrays;
a movable section arranged in the space and including a first electrode section facing the first and second electrode arrays and a second electrode section facing the third and fourth electrode arrays, the first and second electrode sections being maintained at a predetermined floating potential; and
a driving circuit configured to apply DC voltage signals to the first, second, third and fourth electrode arrays, alternatively, the DC voltage signal having a first level higher than the predetermined floating potential and a second level lower than the predetermined floating potential,
the first DC voltage being applied to the first electrodes of the first and second electrode arrays to attract the first electrode section of the movable section during a first period, the first electrodes of the first and second electrode arrays being maintained at the first and second levels during the first period, respectively,
the second DC voltage being applied to the third electrodes of the third and fourth electrode arrays to attract the second electrode section of the movable section during a second period, the third electrodes of the third and fourth electrode arrays being maintained at the first and second levels during the second period, respectively,
the third DC voltage being applied to the second electrodes of the first and second electrode arrays to attract the first electrode section of the movable section during a third period, the second electrodes of the first and second electrode arrays being maintained at the first and second levels during the third period, respectively,
the fourth DC voltage being applied to the fourth electrodes of the third and fourth electrode arrays to attract the second electrode section of the movable section during a fourth period, the fourth electrodes of the third and fourth electrode arrays being maintained at the first and second levels during the third period, respectively, and
the movable section being moved in the first direction in accordance with the application of the first, second, third and fourth DC voltage signals.
According to a fifth aspect of the present invention, there is provided an electrostatic actuator, comprising:
a first stator section including first, second and third electrode arrays each including first and second electrodes and arranged substantially in parallel and at a predetermined pitch in a first direction;
a second stator section arranged to face the first stator section and to define a space between the first and second stator sections, and including a fourth electrode array including fourth and fifth electrodes;
a movable section arranged in the space and including a first electrode section facing the first, second and third electrode arrays and a second electrode section facing the fourth and fifth electrode arrays, the first and second electrode sections being maintained at a predetermined floating potential; and
a driving circuit configured to apply DC voltage signals to the first, second, third and fourth electrode arrays, alternatively, the DC voltage signal having a first level higher than the predetermined floating potential and a second level lower than the predetermined floating potential,
the first DC voltage signal being applied to the first electrodes of the first, second and third electrode arrays to attract the first electrode section of the movable section during a first period, the first electrodes of the first and third electrode arrays being maintained at one of the first and second levels during the first period and the first electrode of the second electrode array being maintained at the other of the first and second levels during the first period,
the second DC voltage signal being applied to the third and fourth electrodes of the fourth electrode array to attract the second electrode section of the movable section during a second period,
the third DC voltage signal being applied to the second electrodes of the first, second and third electrode arrays to attract the first electrode section of the movable section during a third period, the second electrodes of the first and third electrode arrays being maintained at one of the first and second levels during the third period, the second electrodes of the second electrode array being maintained at the other of the first and second levels during the third period, and the movable section being moved in the first direction in accordance with the application of the first, second and third DC voltage signals.
According to a sixth aspect of the present invention, there is provided a camera module for photographing a picture image, comprising:
an electrostatic actuator, including:
a first stator section including a first electrode array including first, second and third electrodes arranged at a predetermined pitch in a first direction;
a second stator section arranged to face the first stator section and to define a space between the first and second stator sections, and including a second electrode array including fourth and fifth electrodes extending in the first direction;
a movable section arranged in the space and including a first electrode section facing the first electrode array and a second electrode section facing the second electrode array, the first and second electrode sections being maintained at a predetermined floating potential; and
a driving circuit configured to apply DC voltage signals to the first and second electrode arrays, alternatively, the DC voltage signal having a first level higher than the predetermined floating potential and a second level lower than the predetermined floating potential,
the first DC voltage signal being applied to the adjacent first and second electrodes of the first electrode array to attract the first electrode section of the movable section during a first period, the first and second electrodes of the first electrode array being maintained at the first and second levels during the first period, respectively,
the second DC voltage signal being applied to the fourth and fifth electrodes of the second electrode array to attract the second electrode section of the movable section during a second period, the fourth and fifth electrodes of the second electrode array being maintained at the first and second levels during the second period, respectively,
the third DC voltage signal being applied to the adjacent second and third electrodes of the first electrode array to attract the first electrode section of the movable section during a third period, the second and third electrodes of the first electrode array being maintained at the first and second levels during the third period, respectively,
the fourth DC voltage signal being applied to the fourth and fifth electrodes of the second electrode array to attract the second electrode section of the movable section during a fourth period, the fourth electrode of the second electrode array being maintained at one of the first and second levels during the fourth period, and the fifth electrode of the second electrode array being maintained at the other of first and second levels during the fourth period, and
the movable section being moved in the first direction in accordance with the application of the first, second, third and fourth DC voltage signals;
a lens mounted in the movable section and movable with the movable section, configured to transfer the picture image; and
an image pick-up element configured to receive the transferred picture image to generate a image signal.
According to a seventh aspect of the present invention, there is provided a camera module for photographing a picture image, comprising:
an electrostatic actuator, including:
a first stator section including a first electrode array including first, second and third electrodes arranged at a predetermined pitch in a first direction;
a second stator section arranged to face the first stator section and to define a space between the first and second stator sections, and including a second electrode array including fourth, fifth and sixth electrodes arranged at the predetermined pitch in the first direction;
a movable section arranged in the space and including a first electrode section facing the first electrode array and a second electrode section facing the second electrode array, the first and second electrode sections being maintained at a predetermined floating potential; and
a driving circuit configured to apply DC voltage signals to the first and second electrode arrays, alternatively, the DC voltage signal having a first level higher than the predetermined floating potential and a second level lower than the predetermined floating potential,
the first DC voltage signal being applied to the adjacent first and second electrodes of the first electrode array to attract the first electrode section of the movable section during a first period, the first and second electrodes of the first electrode array being maintained at the first and second levels during the first period, respectively,
the second DC voltage signal being applied to the adjacent fourth and fifth electrodes of the second electrode array to attract the second electrode section of the movable section during a second period, the fourth and fifth electrodes of the second electrode array being maintained at the first and second levels during the second period, respectively,
the third DC voltage signal being applied to the adjacent second and third electrodes of the first electrode array to attract the first electrode section of the movable section during a third period, the second and third electrodes of the first electrode array being maintained at the first and second levels during the third period, respectively,
the fourth DC voltage signal being applied to the adjacent fifth and sixth electrodes of the second electrode array to attract the second electrode section of the movable section during a fourth period, the fifth and sixth electrodes of the second electrode array being maintained at the first and second levels during the fourth period, respectively, and
the movable section being moved in the first direction in accordance with the application of the first, second, third and fourth DC voltage signals;
a lens mounted in the movable section and movable with the movable section, configured to transfer the picture image; and
an image pick-up element configured to receive the transferred picture image to generate a image signal.
According to a eighth aspect of the present invention, there is provided a camera module for photographing a picture image, comprising:
an electrostatic actuator, including:
a first stator section including first and second electrode arrays each including first and second electrodes and arranged substantially in parallel and at a predetermined pitch in a first direction;
a second stator section arranged to face the first stator section and to define a space between the first and second stator sections, and including third and fourth electrode arrays each including third and fourth electrodes and arranged substantially in parallel and at a predetermined pitch in the first direction, the third and fourth electrode array being arranged at the same pitch as that of the first and second electrode arrays in the first direction and the arrangement of the third and fourth electrode arrays being deviated by the half of the predetermined pitch from the arrangement of the first and second electrode arrays;
a movable section arranged in the space and including a first electrode section facing the first and second electrode arrays and a second electrode section facing the third and fourth electrode arrays, the first and second electrode sections being maintained at a predetermined floating potential; and
a driving circuit configured to apply DC voltage signals to the first, second, third and fourth electrode arrays, alternatively, the DC voltage signal having a first level higher than the predetermined floating potential and a second level lower than the predetermined floating potential,
the first DC voltage being applied to the first electrodes of the first and second electrode arrays to attract the first electrode section of the movable section during a first period, the first electrodes of the first and second electrode arrays being maintained at the first and second levels during the first period, respectively,
the second DC voltage being applied to the third electrodes of the third and fourth electrode arrays to attract the second electrode section of the movable section during a second period, the third electrodes of the third and fourth electrode arrays being maintained at the first and second levels during the second period, respectively,
the third DC voltage being applied to the second electrodes of the first and second electrode arrays to attract the first electrode section of the movable section during a third period, the second electrodes of the first and second electrode arrays being maintained at the first and second levels during the third period, respectively,
the fourth DC voltage being applied to the fourth electrodes of the third and fourth electrode arrays to attract the second electrode section of the movable section during a fourth period, the fourth electrodes of the third and fourth electrode arrays being maintained at the third and fourth levels during the fourth period, respectively, and
the movable section being moved in the first direction in accordance with the application of the first, second, third and fourth DC voltage signals;
a lens mounted in the movable section and movable with the movable section, configured to transfer the picture image; and
an image pick-up element configured to receive the transferred picture image to generate a image signal.
According to a ninth aspect of the present invention, there is provided a camera module for photographing a picture image, comprising:
an electrostatic actuator, including:
a first stator section including first, second and third electrode arrays each including first and second electrodes and arranged substantially in parallel and at a predetermined pitch in a first direction;
a second stator section arranged to face the first stator section and to define a space between the first and second stator sections, and including a fourth electrode array including fourth and fifth electrodes;
a movable section arranged in the space and including a first electrode section facing the first, second and third electrode arrays and a second electrode section facing the fourth electrode array, the first and second electrode sections being maintained at a predetermined floating potential; and
a driving circuit configured to apply DC voltage signals to the first, second, third and fourth electrode arrays, alternatively, the DC voltage signal having a first level higher than the predetermined floating potential and a second level lower than the predetermined floating potential,
the first DC voltage signal being applied to the first and second electrodes of the first, second and third electrode arrays to attract the first electrode section of the movable section during a first period, the first and second electrodes of the first and third electrode arrays being maintained at one of the first and second levels during the first period and the first and second electrodes of the second electrode array being maintained at the other of the first and second levels during the first period,
the second DC voltage signal being applied to the third and fourth electrodes of the fourth electrode array to attract the second electrode section of the movable section during a second period,
the third DC voltage signal being applied to the second and third electrodes of the first, second and third electrode arrays to attract the first electrode section of the movable section during a third period, the second and third electrodes of the first and third electrode arrays being maintained at one of the first and second levels during the third period, the second electrodes of the second electrode array being maintained at the other of the first and second levels during the third period, and the movable section being moved in the first direction in accordance with the application of the first, second and third DC voltage signals;
a lens mounted in the movable section and movable with the movable section, configured to transfer the picture image; and
an image pick-up element configured to receive the transferred picture image to generate a image signal.